In implant dentistry, the procedure of image guided surgery is as following. An impression of a patient is taken at a dental office. It is then sent to a lab to make a radiographic guide (also known as scan template). The patient and the guide are sent to image center for CT or cone beam CT (CBCT) scan. The scan images are input into the treatment planning software that creates a treatment plan. Sometimes the radiographic guide is not necessary, so the treatment plan is just based on the patient's CT scan. The end result of treatment planning would be to design and make a surgical guide, a device with drilling sleeves for all the implants. It is placed onto patient's jawbone or mucosa at surgery time so that the surgeon can use it as a guide to drill holes for implant sites. If the treatment plan specifies, a surgical kit will be also used. Orentlicher et al. (US 2007/0059665 A1) described a similar procedure for obtaining patient image data for planning and/or placing dental implants. The patient is scanned at a radiology facility. Image data is then forwarded to a processing center and converted into a file of different format, which is later on forwarded to doctor's office for treatment planning.
In a typical dental implant planning system, a jawbone model, or a radiographic guide model if available, is used as a base for the surgical guide design. The user chooses the implant platforms (make, model and size), places implants as desired, and specifies a surgical kit to be used. The entire treatment plan with all of such information is sent to a manufacturing facility, where CAD operations are applied onto either the base model or even the filtered CT image data to create a surgical guide. The operations will create holes, inspection windows and other form features. The positions, orientations and sizes of implants, as well as the choice of the surgical kit, determine these modeling operations. The surgical guide is then made with CAM technology.
With almost all the dental implant planning systems, the treatment plans are sent to the vendors' facilities for further surgical guide design and manufacturing. The design and manufacturing happen behind the scene. The vendors mainly include NobelBiocare, Materialise, I-Dent, Keystone Dental, etc. Such a workflow is illustrated in FIG. 1. The review of the state-of-art treatment planning technologies can be found in the publications of Tardieu PB, Azari A, Jabero M, Spector L, etc. Some of them are listed in the references section.
One of the major disadvantages of this workflow is that the links between the steps are broken. When a doctor's office receives a processed model, they cannot do anything to change it. After they have started the planning, if they find the processed model doesn't well represent the patient's bone structure, they either keep going at a great risk without correcting the model, or request a new processing and hence lose their work. This problem also exists in the design of the surgical guide after the planning is done. Once the design starts, plan changes are not easy.
In this sequential workflow from image processing to treatment planning and then to surgical guide design, there is a pending issue that all the data and operation history should be kept, and any changes in an earlier stage can be propagated to later ones with the operations in later stages automatically updated. This is called an associative workflow or associativity in the workflow.
As far as surgical guide CAD/CAM is concerned, very rare information has been disclosed. Swaelens (U.S. Pat. No. 5,768,134) disclosed a method to make “perfected medical model” on the basis of medical image information with rapid prototyping technology. The approach starts with images of a part of the body of a patient by means of a CT scan or the like. Artificial functional elements corresponding to implant plans are added into the image data in a voxel-based method in the module that controls rapid prototyping. It was mentioned that the voxel based perfect model with functional elements could be converted to STL (triangle format) or moved into CAD systems to further add elements. This invention does not really concern a CAD approach commonly found in many industries, nor provides any user controls for the manipulation of the model. It provides some hybrid process of image processing, rapid prototyping, as well as modifying the image data with functional elements that are also voxel based. Since it encapsulates the operations to add form features by voxels into the rapid prototyping procedure, it does not integrate CAD and CAM in a conventional way where CAD and CAM are independent systems or modules. Also it is not clear how the “voxel-based” approach is used to add functional elements to the image data. In the final surgical guide model the smoothness/accuracy of the implant holes are much higher than CT data. In order to create holes like this, the voxels will have to be in the 20-40 microns range. However, the image data of the CT scan normally has voxel size of 200 microns up to 1 mm. It would be extremely computation extensive to reformat the CT scan to the acceptable accuracy.
In contrast, Keystone Dental directly drill holes and make other features off the radiographic guide. It is unknown if they actually performs CAD, CAM and the integration of the two.
Roose (US 2005/0148823) describes a method and system to design surgical guides for joint replacement prosthesis. The system includes a bone surface image generator, surgical guide image generator, and surgical guide image converter.
One of the major problems with surgical guide models of the state-of-the-art is the manufacturability and applicability. There are basically two categories of surgical guides. One is based on prefabricated radiographic guides. Another one is based on the bone structures segmented from patients' CT scans. Theoretically there can be a combination of the two approaches. Surgical guides are called tissue-borne for the first category, bone- or tooth-borne for the second. The manufacturability problem is mainly pertinent to the second. Swaelens did mention the perfected model could come from a scan template, but the invention in the way it is presented is mainly concerned of the bone- or tooth-borne guides. So does Roose's application.
It is problematic to design surgical guides based on bone structures hoping the guides will perfectly match the surfaces of the bone structures. Bone segmentation typically does not lead to a smooth model, especially when the patients don't have jaw bones that are dense enough. FIG. 9 shows that the actual bone structure has small dents or holes. This is not the worst case at all. There are situations that the bone quality is much more problem-prone. The surgical guide will have spikes or protrusions if made to match the surface of such a bone structure. It is necessary to cleanup the model in order to properly place it onto patients bone structure during surgery. This is one of the reasons that design of surgical guides will need to have the considerations for both manufacturability and applicability.
The accuracy of the surgical guide models is another critical issue. Due to many reasons, the reconstructed surface model of a scan template, or the contour surface of a bone structure, is barely accurate enough for the final surgical guide. Please see the application recently filed (Gao, 12,776,544). An iteration approach with calibration features is disclosed in that application, which also presents a legitimate reason that the associativity between image processing and guide design is necessary.
Another issue related to implant planning is the use of surgical kits. The introduction of surgical guides cannot be isolated from surgical kits. Implant surgical kits help the surgeons to drill holes with better orientation and depth control. Not like the old time that implants sites are all prepared with freehand drilling, nowadays surgical kits have components and features to ensure better operations. For example, adaptors or keys let the surgeon to fit different drills into one prepared hole, and thus facilitate sequential drilling without repositioning the tools. Drill stops, special features added to the drills, help the surgeons to control the depth of their drilling. As a result of using surgical kits, surgical guides are designed corresponding to the kits, and drill instructions are generated by treatment planning systems accordingly. More information about dental implant surgical kits can be found at NobelBiocare and other vendors' websites.
Software vendors typically let the users choose a platform of surgical kits, and generate the surgical guide models accordingly. The guide design is determined by both the treatment plan and the surgical kits chosen by the treatment planner. The popular approach is to design one surgical guide for each case. All the drilling sequences are performed with this guide and the selected surgical kits. Some systems only generate a guide for pilot drills, and let the surgeons do freehand drilling for the rest of the drilling sequences. Some systems generate multiple guides for a case, one guide for one drilling step of the sequences. More related information can be found in the websites of Materialise and NobelBiocare.
Berckmans, III et al. (US 2009/0263764 A1) introduces a method to design a surgical guide so that the surgical kit can certainly fit into the patient's mouth. The approach needs the patient's CT scan with mouth opened.
With the state-of-art techniques, users are not given the access to the computer aided design system of surgical guides, so what can be done is to just let users choose surgical kit platforms. In an open architecture and an integrated solution where the users are given the control to the entire planning and design process, there will be a need for the users to define or configure a surgical kit of their own, and adjust their guide design accordingly. For this purpose a universal definition of surgical kits is desired.
With prior art, one surgical kit is selected for one case, and the surgical guide is made for this kit. Sometimes, the guide is designed without the consideration of a kit simply because no kit is available. However, there can be situations that a doctor believes two implants of different models or even from different vendors need to be used in a single case. First, it can be for clinical reasons. The doctor decides to do so for the feasibility and survivability of the implants. The second reason can be that the patient's anatomical structure cannot accommodate certain surgical kit very well, or the guide model generated from the kit is considered not usable. Thirdly, surgical kits are normally designed for specific implant platforms, such as NobelBiocare's NobelReplace NP, RP, etc, thus are only applicable for the implants of given types and sizes. There are far more implant platforms than surgical kits, therefore there are scenarios that only some of the implants of a case can use surgical kits, or, scenarios that some implants may use one kit, some use another. Such scenarios have not been considered in prior art or publications yet. They don't happen very often, but are possible.
In summary, the following issues need to be resolved in order to have a good treatment planning solution. An associative workflow is desired to integrate image processing, treatment planning and surgical guide CAD/CAM. Surgical guide models need to be free from artifacts stemming from the patients bone density deficiency and structural problems so that the manufacturing of surgical guides can be done with common CAM solutions from RP to milling. An open architecture is needed for the users to configure their surgical kits in a universal way and for system to drive the guide design. This invention addresses these issues and develops approaches and software system to solve them.